bit·ter / ˈbitər/ • adj. 1. having a sharp, pungent taste or smell; not sweet: the raw berries have an intensely bitter flavor. ∎  (of chocolate) dark and unsweetened.2. (of people or their feelings or behavior) angry, hurt, or resentful because of one's bad experiences or a sense of unjust treatment: I don't feel jealous or bitter.3. harsh or unpleasant, in particular: ∎  (often used for emphasis) painful or unpleasant to accept or contemplate: today's decision has come as a bitter blow. ∎  (of a conflict, argument, or opponent) full of anger and acrimony: a bitter, five-year legal battle. ∎  (of wind, cold, or weather) intensely cold: a bitter wind blowing from the east.• n. 1. [mass noun] Brit. beer that is strongly flavored with hops and has a bitter taste.2. (bitters) [treated as sing] liquor that is flavored with the sharp pungent taste of plant extracts and is used in cocktails or to promote appetite or digestion.PHRASES: to the bitter end used to say that one will continue doing something until it is finished, no matter what: the workers would fight to the bitter end for safer conditions.DERIVATIVES: bit·ter·ly adv.bit·ter·ness n.

bitter1 contrary of sweet. OE. biter, corr. to OS., OHG. bittar (Du., G. bitter), ON. bitr, Goth. baitrs; prob. f. Gmc. *bit-, base of *bītan BITE.
Hence bitter-sweet sb. XIV, adj. XVII. cf. F. aigre-doux, amer-doux. L. dulcamārum. So bitterly OE. biterlīce; see -LY2. bitterness OE. biternes.

bitter2 ‘a Bitter is but the turn of a Cable about the Bitts. . And the Bitters end is that part of the Cable doth stay within boord’ (1627, Capt Smith). f. BITT + -ER1.
Hence prob. phr. to the bitter end to the last extremity (now assoc. with BITTER1).

bitter Traditional British beer with a bitter flavour due to its content of hops.